Control Structures: Part 1

© 2003 Prentice Hall, Inc. All rights reserved.
1
Outline
4.1 Introduction
4.2 Algorithms
4.3 Pseudocode
4.4 Control Structures
4.5 if Single-Selection Statement
4.6 if else Selection Statement
4.7 while Repetition Statement
4.8 Formulating Algorithms: Case Study 1 (Counter-
Controlled Repetition)
4.9 Formulating Algorithms with Top-Down, Stepwise
Refinement: Case Study 2 (Sentinel-Controlled Repetition)
4.10 Formulating Algorithms with Top-Down, Stepwise
Refinement: Case Study 3 (Nested Control Structures)
4.11 Compound Assignment Operators
4.12 Increment and Decrement Operators
4.13 Primitive Types
4.14 (Optional Case Study) Thinking About Objects: Identifying
Class Attributes
Chapter 4 - Control Structures: Part 1

2
4.1 Introduction
• We learn about Control Structures
– Structured-programming principle
– Control structures help build and manipulate objects
(Chapter 8)

3
4.2 Algorithms
• Algorithm
– Series of actions in specific order
• The actions executed
• The order in which actions execute
• Program control
– Specifying the order in which actions execute
• Control structures help specify this order

4
4.3 Pseudocode
• Pseudocode
– Informal language for developing algorithms
– Not executed on computers
– Helps developers “think out” algorithms

5
• Sequential execution
– Program statements execute one after the other
• Transfer of control
– Three control statements can specify order of statements
• Sequence structure
• Selection structure
• Repetition structure
• Activity diagram
– Models the workflow
• Action-state symbols
• Transition arrows

6
Fig 4.1 Sequence structure activity diagram.
add grade to total
add 1 to counter
Corresponding Java statement:
total = total + grade;
counter = counter + 1;

7
Java Keywords
abstract assert boolean break byte
case catch char class continue
default do double else extends
final finally float for if
implements import instanceof int interface
long native new package private
protected public return short static
strictfp super switch synchronized this
throw throws transient try void
volatile while
Keywords that are reserved, but not currently used
const goto
Fig. 4.2 Java keywords.

8
• Java has a sequence structure “built-in”
• Java provides three selection structures
– if
– If…else
– switch
• Java provides three repetition structures
– while
– do…while
– do
• Each of these words is a Java keyword

9
4.5 if Single-Selection Statement
• Single-entry/single-exit control structure
• Perform action only when condition is true
• Action/decision programming model

10
Fig 4.3 if single-selections statement activity diagram.
[grade >= 60]
[grade < 60]
print “Passed”

11
4.6 if…else Selection Statement
• Perform action only when condition is true
• Perform different specified action when condition
is false
• Conditional operator (?:)
• Nested if…else selection structures

12
Fig 4.4 if…else double-selections statement activity diagram.
[grade >= 60][grade < 60]
print “Failed” print “Passed”

13
4.7 while Repetition Statement
• Repeat action while condition remains true

14
Fig 4.5 while repetition statement activity diagram.
[product <= 1000]
[product > 1000]
double product value
merge
decision
product = 2 * product;

15
4.8 Formulating Algorithms: Case Study 1
(Counter-Controlled Repetition)
• Counter
– Variable that controls number of times set of statements
executes
• Average1.java calculates grade averages
– uses counters to control repetition

16

Set total to zero
Set grade counter to one
While grade counter is less than or equal to ten
Input the next grade
Add the grade into the total
Add one to the grade counter
Set the class average to the total divided by ten
Print the class average
Fig. 4.6 Pseudocode algorithm that uses counter-
controlled repetition to solve the class-average
problem.

© 2003 Prentice Hall, Inc.
All rights reserved.
Outline
17
Average1.java
gradeCounter
Line 21
1 // Fig. 4.7: Average1.java
2 // Class-average program with counter-controlled repetition.
3 import javax.swing.JOptionPane;
4
5 public class Average1 {
6
7 public static void main( String args[] )
8 {
9 int total; // sum of grades input by user
10 int gradeCounter; // number of grade to be entered next
11 int grade; // grade value
12 int average; // average of grades
13
14 String gradeString; // grade typed by user
15
16 // initialization phase
17 total = 0; // initialize total
18 gradeCounter = 1; // initialize loop counter
19
20 // processing phase
21 while ( gradeCounter <= 10 ) { // loop 10 times
22
23 // prompt for input and read grade from user
24 gradeString = JOptionPane.showInputDialog(
25 "Enter integer grade: " );
26
27 // convert gradeString to int
28 grade = Integer.parseInt( gradeString );
29
Declare variables;
gradeCounter is the counter
Continue looping as long as
gradeCounter is less than or
equal to 10

Outline
18
Average1.java
30 total = total + grade; // add grade to total
31 gradeCounter = gradeCounter + 1; // increment counter
32
33 } // end while
34
35 // termination phase
36 average = total / 10; // integer division
37
38 // display average of exam grades
39 JOptionPane.showMessageDialog( null, "Class average is " + average,
40 "Class Average", JOptionPane.INFORMATION_MESSAGE );
41
42 System.exit( 0 ); // terminate the program
43
44 } // end main
45
46 } // end class Average1

Outline
19
Average1.java

204.9 Formulating Algorithms with Top-Down,
Stepwise Refinement: Case Study 2
(Sentinel-Controlled Repetition)
• Sentinel value
– Used to indicated the end of data entry
• Average2.java has indefinite repetition
– User enters sentinel value (-1) to end repetition

21
Initialize total to zero
Initialize counter to zero
Input the first grade (possibly the sentinel)
While the user has not as yet entered the sentinel
Add this grade into the running total
Add one to the grade counter
Input the next grade (possibly the sentinel)
If the counter is not equal to zero
Set the average to the total divided by the counter
Print the average
else
Print “No grades were entered”
Fig. 4.8 Class-average problem pseudocode
algorithm with sentinel-controlled repetition.

Outline
22
Average2.java
1 // Fig. 4.9: Average2.java
2 // Class-average program with sentinel-controlled repetition.
3 import java.text.DecimalFormat; // class to format numbers
5
6 public class Average2 {
7
9 {
10 int total; // sum of grades
11 int gradeCounter; // number of grades entered
12 int grade; // grade value
13
14 double average; // number with decimal point for average
15
16 String gradeString; // grade typed by user
17
18 // initialization phase
19 total = 0; // initialize total
20 gradeCounter = 0; // initialize loop counter
21
22 // processing phase
23 // get first grade from user
25 "Enter Integer Grade or -1 to Quit:" );
26
29

Outline
23
Average2.java
Line 31
Line 45
30 // loop until sentinel value read from user
31 while ( grade != -1 ) {
32 total = total + grade; // add grade to total
33 gradeCounter = gradeCounter + 1; // increment counter
34
35 // get next grade from user
37 "Enter Integer Grade or -1 to Quit:" );
38
41
42 } // end while
43
44 // termination phase
45 DecimalFormat twoDigits = new DecimalFormat( "0.00" );
46
47 // if user entered at least one grade...
48 if ( gradeCounter != 0 ) {
49
50 // calculate average of all grades entered
51 average = (double) total / gradeCounter;
52
53 // display average with two digits of precision
54 JOptionPane.showMessageDialog( null,
55 "Class average is " + twoDigits.format( average ),
57
58 } // end if part of if...else
59
loop until gradeCounter
equals sentinel value (-1)
Format numbers to nearest
hundredth

Outline
24
Average2.java
60 else // if no grades entered, output appropriate message
61 JOptionPane.showMessageDialog( null, "No grades were entered",
63
64 System.exit( 0 ); // terminate application
65
66 } // end main
67
68 } // end class Average2

254.10 Formulating Algorithms with Top-Down,
Stepwise Refinement: Case Study 3
(Nested Control Structures)
• Nested control structures

26
Initialize passes to zero
Initialize failures to zero
Initialize student to one
While student counter is less than or equal to ten
Input the next exam result
If the student passed
Add one to passes
else
Add one to failures
Add one to student counter
Print the number of passes
Print the number of failures
If more than eight students passed
Print “Raise tuition”
Fig 4.10 Pseudocode for examination-results problem.

Outline
27
Analysis.java
Line 19
Line 29
1 // Fig. 4.11: Analysis.java
2 // Analysis of examination results.
4
5 public class Analysis {
6
8 {
9 // initializing variables in declarations
10 int passes = 0; // number of passes
11 int failures = 0; // number of failures
12 int studentCounter = 1; // student counter
13 int result; // one exam result
14
15 String input; // user-entered value
16 String output; // output string
17
18 // process 10 students using counter-controlled loop
19 while ( studentCounter <= 10 ) {
20
21 // prompt user for input and obtain value from user
22 input = JOptionPane.showInputDialog(
23 "Enter result (1 = pass, 2 = fail)" );
24
25 // convert result to int
26 result = Integer.parseInt( input );
27
28 // if result 1, increment passes; if...else nested in while
29 if ( result == 1 )
30 passes = passes + 1;
Loop until student counter is
greater than 10
Nested control structure

Outline
28
Analysis.java
31
32 else // if result not 1, increment failures
33 failures = failures + 1;
34
35 // increment studentCounter so loop eventually terminates
36 studentCounter = studentCounter + 1;
37
38 } // end while
39
40 // termination phase; prepare and display results
41 output = "Passed: " + passes + "nFailed: " + failures;
42
43 // determine whether more than 8 students passed
44 if ( passes > 8 )
45 output = output + "nRaise Tuition";
46
47 JOptionPane.showMessageDialog( null, output,
48 "Analysis of Examination Results",
49 JOptionPane.INFORMATION_MESSAGE );
50
51 System.exit( 0 ); // terminate application
52
53 } // end main
54
55 } // end class Analysis

29
4.11 Compound Assignment Operators
• Assignment Operators
– Abbreviate assignment expressions
– Any statement of form
• variable = variable operator expression;
– Can be written as
• variable operator= expression;
– e.g., addition assignment operator +=
• c = c + 3
– can be written as
• c += 3

30
Assignment
operator
Sample
expression
Explanation Assigns
Assume: int c = 3,
d = 5, e = 4, f
= 6, g = 12;
+= c += 7 c = c + 7 10 to c
-= d -= 4 d = d - 4 1 to d
*= e *= 5 e = e * 5 20 to e
/= f /= 3 f = f / 3 2 to f
%= g %= 9 g = g % 9 3 to g
Fig. 4.12 Arithmetic assignment operators.

31
4.12 Increment and Decrement Operators
• Unary increment operator (++)
– Increment variable’s value by 1
• Unary decrement operator (--)
– Decrement variable’s value by 1
• Preincrement / predecrement operator
• Post-increment / post-decrement operator

32
Operator Called Sample
expression
Explanation
++ preincrement ++a Increment a by 1, then use the new
value of a in the expression in
which a resides.
++ postincrement a++ Use the current value of a in the
expression in which a resides, then
increment a by 1.
-- predecrement --b Decrement b by 1, then use the
new value of b in the expression in
which b resides.
-- postdecrement b-- Use the current value of b in the
expression in which b resides, then
decrement b by 1.
Fig. 4.13 The increment and decrement operators.

Outline
33
Increment.java
Line 13 postincrement
Line 21 preincrement
1 // Fig. 4.14: Increment.java
2 // Preincrementing and postincrementing operators.
3
4 public class Increment {
5
7 {
8 int c;
9
10 // demonstrate postincrement
11 c = 5; // assign 5 to c
12 System.out.println( c ); // print 5
13 System.out.println( c++ ); // print 5 then postincrement
15
16 System.out.println(); // skip a line
17
18 // demonstrate preincrement
19 c = 5; // assign 5 to c
21 System.out.println( ++c ); // preincrement then print 6
23
24 } // end main
25
26 } // end class Increment
5
5
6
5
6
6
Line 13 postincrements c
Line 21 preincrements c

34
Operators Associativity Type
++ -- right to left unary postfix
++ -- + - (type) right to left unary
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
?: right to left conditional
= += -= *= /= %= right to left assignment
Fig. 4.15 Precedence and associativity of the operators discussed so far.

35
4.13 Primitive Types
• Primitive types
– “building blocks” for more complicated types
• Java is strongly typed
– All variables in a Java program must have a type
• Java primitive types
– portable across computer platforms that support Java

36
Type Size in bits Values Standard
boolean true or false
[Note: The representation of a boolean is
specific to the Java Virtual Machine on each
computer platform.]
char 16 'u0000' to 'uFFFF'
(0 to 65535)
(ISO Unicode character set)
byte 8 –128 to +127
(–27
to 27
– 1)
short 16 –32,768 to +32,767
(–215
to 215
– 1)
int 32 –2,147,483,648 to +2,147,483,647
(–231
to 231
– 1)
long 64 –9,223,372,036,854,775,808 to
+9,223,372,036,854,775,807
(–263
to 263
– 1)
float 32 Negative range:
–3.4028234663852886E+38 to
–1.40129846432481707e–45
Positive range:
1.40129846432481707e–45 to
3.4028234663852886E+38
(IEEE 754 floating point)
double 64 Negative range:
–1.7976931348623157E+308 to
–4.94065645841246544e–324
Positive range:
4.94065645841246544e–324 to
1.7976931348623157E+308
(IEEE 754 floating point)
Fig. 4.16The Java primitive types.

37
4.14 (Optional Case Study) Thinking About
Objects: Identifying Class Attributes
• Classes have attributes (data)
– Implemented in Java programs as variables
– Attributes of real-world objects
• Radio (object)
– Station setting, volume setting, AM or FM (attributes)
• Identify attributes
– Look for descriptive words and phrases in problem statement
– Each identified word and phrase is a candidate attribute
• e.g., “the elevator is moving”
– “is moving” corresponds to boolean attribute moving
• e.g., “the elevator takes five seconds to travel between floors”
– corresponds to int attribute travelTime
• int travelTime = 5; (in Java)

38
Class Descriptive words and phrases
ElevatorShaft [no descriptive words or phrases]
Elevator moving
summoned
current floor
destination floor
capacity of only one person
five seconds to travel between floors
Person unique
waiting / moving
current floor
Floor first or second; capacity for only one person
FloorButton pressed / reset
ElevatorButton pressed / reset
FloorDoor door closed / door open
ElevatorDoor door closed / door open
Bell [no descriptive words or phrases]
Light turned on / turned off
Fig. 4.17 Descriptive words and phrases from problem statement.

39
4.14 (Optional Case Study) Thinking About
Objects: Identifying Class Attributes (Cont.)
• UML class diagram
– Class attributes are place in the middle compartment
– Attributes are written language independently
• e.g., attribute open of class ElevatorDoor
– open : Boolean = false
• May be coded in Java as
– boolean open = false;

40
Fig. 4.18 Classes with attributes.
Person
ID : Integer
moving : Boolean = true
currentFloor : Integer
Elevator
moving : Boolean = false
summoned : Boolean = false
currentFloor : Integer = 1
destinationFloor : Integer = 2
capacity : Integer = 1
travelTime : Integer = 5
ElevatorShaft
Floor
floorNumber : Integer
capacity : Integer = 1
ElevatorButton
pressed : Boolean = false
FloorButton
pressed : Boolean = false
ElevatorDoor
open : Boolean = false
Light
lightOn : Boolean = false
Bell
FloorDoor
open : Boolean = false

Control Structures: Part 1

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